Self soluble slag forming agents for use in steel making

ABSTRACT

An improvement in the manufacture of steel in which a slagforming agent is added to the steel-forming components of a steel refining furnace. The improvement consists of utilizing a slagforming agent consisting essentially of pellets having a composition in percent by weight of 50-80 of CaO, 15-30 of SiO2, 3-7 of Al2O3, and 2-15 of Fe2O3.

Ohkubo et al.

SELF SOLUBLE SLAG FORMING AGENTS FOR USE IN STEEL MAKING Inventors: Masuta Ohkubo; Moriyuki lshiguro, both of Kawasaki, Japan Nippon Kokan Kabushiki Kaisha, Kawasaki-shi, Kanagawa-ken, Japan Filed: Aug. 31, 1972 Appl. No.: 285,475

Related US. Application Data 67.621. Aug. 27.

Assignee:

Division of Ser. No. 1970,

abandoned.

Foreign Application Priority Data Aug. 29, 1969 Japan 44-67947 References Cited UNITED STATES PATENTS 6/1971 Obst 75/53 1 Apr. 9, 1974 3,537,842 11/1970 Holland 75/53 3,288,572 11/1966 Tadsen 75/30 3,426,833 2/1969 Randak 75/53 2,781,256 2/1957 Richards 75/53 2,750,280 6/1956 Perrin 75/55 3,301,663 1/1967 Wicher 75/58 2,779,675 1/1957 Vennerholm... 75/55 3,519,386 11/1965 Fedock 75/94 3,547,622 12/1970 Hutchinson 75/49 Primary E.\'aminerL. Dewayne Rutledge Assistant E.\'aminerPeter D. Rosenberg Attorney, Agent, or Firm-Flynn & Frishauf 5 7] ABSTRACT An improvement in the manufacture of steel in which a slag-forming agent is added to the steel-forming components of a steel refining furnace. The improvement consists of utilizing a slag-fon'ning agent consisting essentially of pellets having a composition in percent by weight of 50-80 of CaO, 15-30 of SiO 3-7 of A1 0 and 2-15 of Fe O 4 Claims, No Drawings SELF SOLUBLE SLAG FORMING AGENTS FOR USE IN STEEL MAKING This application is a divisional application of copending application S.N. 67,621, filed Aug. 27, 1970, which To overcome the disadvantages caused by the use of separate particles of the individual components, the present invention provides a slag forming agent in which particles have approximately the same size and is now abandoned. composition. When expressed in terms of oxide compo- The present invention relates to a slag forming agent sition, particles of a slag forming agent in accordance suitable for use in steel making furnaces such as com with the present invention comprise 50 to 80 percent verters, open-hearth furnaces and electric furnaces, y e g t of C30, 15 to 30 percent by weight Of 2, which agent is a self-soluble type of precalcined CaO 3 to 7 percent by weight of A1 0 and 2 to percent 0 A1 0 F 0 d h excellent l f i 10 by weight of I e- 0 The slag forming agent of the presni ent invention can readily be prepared by compounding Slag forming agents which have heretofore been used and c ining appropriate materials to produce a comin teel making include for example: those Qbposition comprising, when expressed In terms Of oxide tained from naturally occurring ores such as limestone, composltlbni 50 b 8O P b by weight of C30, to fluospar, iron sand, etc. by pulverizing, sieving and/or 15 3O Perbent y Weight of S102, 3 to 7 Percent by welgbt compounding to produce a desired particle size and of 2 3 and 2 to P f y welghi of bz a v and composition, (2) those, as in the case of lime, obtained b q y screemflg to 5126 the gram} Since each by grinding ores, calcining the ground ores without ff of the Slag forming agem b b bptlmum P adding other materials, and screened to size the grains; I 5111011 35 a 8 fbrmmg g b i Self solublfl, and (3) iron oxides such as dusts, scale, etc., produced when "l the lag fbfmatlbn 1t dlssblves yas by-products in plants. Thus, naturally existing mate- The Invention be Illustrated y the p rials as such or those merely calcined to remove CO Exam 1 p e have commonly been used as a slag forming agent, and in exceptional cases several materials are compounded In this p bi a Slag formlbg test was earned but In to give an appropriate co pgsition calcined to pro. a electric furnace using the self-soluble slag duce a material chemically distinct from the individual fbrmmlg agent b Present mvenbbn' starting materials, and then used as a slag forming A clmker, a selfisbluble Slag fb agent agem Calcium f it 0 F6203) has only been of the present invention havmgacompositlon as shown used tentatively v in Table I, was prepared by compounding materials,

As is well known, the purpose of slag forming in a ffiblfbbgffli fflfbiblfig; basic steel making process is to form a molten slag wherein a CaO/SiO ratio is within of range of from TABLE] about 2.5 to about 4, thereby causing impurities in the molten iron, such as P and S, to migrate into the slag, Composition of the clinker by weight) thus removing them from the metal.

For this, lime which has been charged in a solid state 2'86 gf? 3%" should become molten, and, for this purpose, an additional material such as fluospar or scale has heretofore been used together with lime. In a high temperature Using this clinker a steel making process was carried furnace, SiO formed by the oxidation of Si in the mol- 40 out in the small electric furnace described above. ten iron, CaF or iron oxide from the fluospar or the About 300 kg of molten material, and a temperature scale, respectively, and the lime, are re-acted together between l,550 and l,650C. was used. During the proto form a low melting point slag. cess, the state of the slag, behavior of P and S in the Such a method for slag formation according to the molten iron, and time for slag formation were obprior art wherein a high temperature furnace is used to servedjhe resuits areshown in lable ll. react separate particles of lime, scale and fluospar of a TABLEII Operation Time a C a P S State of (min.) (7:) (7c) Slag Melting and Removal of Slag 0 0.68 0.105 0.0l4 None Addition of 20 kg of clinker and 3 kg of Scale l Sampling of Molten iron 10 0.57 0.028 0.0l8 Molten State of Bessemerizing l l Molten End of Bessemerizing l4 Molten Sampling 15 0.24 0.010 0.019 Molten certain size, to form a low melting slag, requires consid- The combination of the clinker and the scale is more erable time and heat, i.e., in dissolving the lime, and in soluble than lime and became molten within 9 minutes consequence the retarded slag formation frequently reeven without bessemerizing. The slag formed had a sults in unsatisfactory dephosphization and desulfurizacomposition wherein the CaO/Si0 ratio was 3.2 and tion. This has been one of the defects of the prior art, reducing the efficiency and productivity of steel mak ing processes. I

dephosphorization proceeded rapidly. 3 minutes of bessemerizing enhanced the contact of slag with metal and caused a further dephosphorization. Concerning sulfur, the content of sulfur in the molten iron increased adversely, presumably because of a high S in the slag forming agent and the oxidizing atmosphere.

As seen from the above example, the self-soluble slag forming agent of the present invention has many advantages. For example, it has superior solubility over a prior art slag forming agent such as lime alone, and has better slag forming properties. The amount of expensive materials such as fluospar, to be used together with a main slag forming agent may be reduced advantageously. For example, if half of the lime to be used is replaced by the cement-like clinker, the amount of fluospar to be used may be reduced to half or less. The invention also contemplates saving expensive lime and converting cheap limestone of low quality and clay into an excellent self-soluble slag forming agent, thus contributing to a cost reduction and improvement of efficiency and productivity in steel making processes.

We claim:

1. In the manufacture of steel in a furnace wherein a slag-forming agent is employed with steel-forming components, the improvement which comprises charging to the furnace a slag-forming agent consisting essentially of uniformly sized particles, each of said particles having a composition, in percent by weight, of 50 to of CaO, 15 to 30 of SiO 3 to 7 of A1 0 and 2 to 15 of Fegog.

2. The manufacture defined by claim 1, wherein the agent has a CaO/SiO ratio of about 3.2.

3. The manufacture defined by claim 1, wherein the agent has the following approximate composition: 65.5 CaO, 23.0 SiO 5.7 A1 0 3.1 Fe O and 1.5 MgO.

4. The manufacture defined by claim 1, wherein the furnace is an electric furnace. 

2. The manufacture defined by claim 1, wherein the agent has a CaO/SiO2 ratio of about 3.2.
 3. The manufacture defined by claim 1, wherein the agent has the following approximate composition: 65.5 CaO, 23.0 SiO2, 5.7 Al2O3, 3.1 Fe2O3 and 1.5 MgO.
 4. The manufacture defined by claim 1, wherein the furnace is an electric furnace. 